This invention pertains to the use of water treatment residuals resulting from drinking water treatment. More specifically, this invention pertains to methods and apparatuses for reusing water treatment residuals, such as alum residuals, generated by drinking water treatment facilities, by converting the alum-type residuals into a form which is more beneficial than has been known heretofore. Alum-type residuals in such a form may be added to other materials to form a blended topsoil.
Water treatment residuals are produced by drinking water supply and purification plants in the treatment process. Such residuals are produced when alum or similar materials are used to cause particulate matter in the water to precipitate. Alum-treated water is then placed in one or more sedimentation basins. While in these basins, the alum associates with raw water turbidity, causing it to precipitate, thereby simultaneously clearing the water and producing alum oi alum-polymer water treatment residual. The cleared water is then removed from the basins for further treatment for use as drinking water. Over time, the water treatment residual accumulates at the bottom of the basins. The residuals are removed from the sedimentation basins and stored in lagoons or tanks. These residuals contain raw water turbidity and unreacted alum and/or alum polymer coagulants and reactive hydroxide compounds. In the past, some alum and alum polymer water treatment residuals have been disposed of in licensed, solid-waste landfill facilities after being de-watered, such as via filter presses at the sites or by other suitable methods. In many states, current state EPA policies prohibit direct land application of alum water treatment residuals. Further, concerns have been raised and associated with landfill disposal of large volumes of alum residuals. While the waste product may not pose imminent hazards to the public or the environment, the presence of alum residuals in a landfill is generally considered to be undesirable.
One alternative to disposing of alum residuals from water treatment facilities has been to reuse the material in the environment as a blended topsoil since the residual is predominantly fine particulate soil components. However, the primary environmental concern associated with alum residual reuse as a soil additive is nutrient binding by the residual. This binding is caused by hydroxides, present in the residual, which bind nutrients such as phosphorus, making them unavailable for use by vegetation.
Another concern with using alum residual is that alum residual contains very limited concentrations of vegetation nutrients in excess of typical soils, and has a diminished value as a low-grade fertilizer in comparison to sewage sludge. However, alum residual has been shown to increase soil moisture holding capacity, which is a major problem associated with course grained or highly organic soils. Additionally, alum residual has been found to reduce the compressive strength of soils, allowing increased root penetration through the soil.
The applicant has recognized the need to provide a process for reusing or recycling alum residuals, particularly alum and alum polymer residuals. Potential uses for alum-type residuals have been considered, mainly compost blending, landfill cover material blending, land application, and topsoil blending.
Compost blending involves blending alum-type residuals with composted materials prior to sale or reuse as an enhanced topsoil material. Composted material contains many nutrients that enhance the ability of soil to sustain vegetation. However, because compost materials originate from decayed organic materials, the compost materials are more acidic than typical soils. Acidic soil conditions can cause metals to be placed in solution, creating a toxic soil condition known as phytotoxicity.
Landfill cover material blending involves blending alum residuals with materials used as cover materials at licensed solid waste disposal facilities. Currently, there is a very limited supply of materials suitable for landfill covers that are also capable of sustaining vegetation. Unprocessed alum residual, however, may not be suitable due to the presence of hydroxides noted above and concomitant nutrient binding. However, use of residuals in a waste disposal facility would allow residuals to be comingled with regulated wastes, potentially creating future remediation liability.
Direct land application involves applying dry or gelatinous alum-type residuals directly to the surface of land, such as farmland, for example. The alum-type residual may be applied to the land and later plowed into the soil to blend the alum-type residual and natural soil. Such applications are of detrimental, however, because of the gelatinous nature of alum-type residual and the potential for nutrient binding. Application of the gelatinous alum-type residual will preclude adequate mixing of the residual with the soil, leaving the alum-type residual in large clumps at or near the surface of the soil after plowing. The potential for nutrient binding by hydroxides also makes this use unattractive, especially for farmland. Additionally, in many states, current state EPA policy prohibits direct land application of such alum-type residuals. Topsoil blending involves blending alum-type residual with topsoil prior to sale or reuse as landscaping topsoil. Topsoil blending would not involve licensed waste facilities, and therefore, would pose a much lower risk for long term liability exposure than landfill cover material blending. Current methods of processing, however, are not well suited for large or small scale use because alum residuals must be granular and sufficiently dewatered for blending. Previous attempts at using alum residual as a soil additive were unable to overcome the limitations of nutrient binding caused by the presence of hydroxides.
It is therefore an object of the present invention to provide an improved method of processing alum-type residuals resulting from the treatment of water for the production of potable water.
It is another object of the present invention to provide alum-type residual in a form that is easier to work and blend with other materials than those that have been known heretofore.
It is still another object of the present invention to provide an alum-type residual with less potential for adverse chemical interactions upon mixing with other materials.
It is yet another object of the present invention to provide a process for the use of alum-type residuals from a drinking water treatment facility by processing alum-type residuals into a form which is easier to work and less reactive than previously known forms, and blending the alum-type residual with topsoil components.
It is still another object of the present invention to provide an improved blended topsoil product with improved physical properties comprising alum-type residuals and top soil components.
These and other objectives are achieved by providing a more thorough and economical method of conditioning alum-type residual than was previously known. This invention also provides a processed alum-type residual that has less reactive hydroxide components than previously known alum-type residuals. The processed alum-type residual of the present invention is also more easily mixed with other materials due to the granular texture of the processed alum-type residual. This granular texture and decreased water content of the processed residual of the present invention provides a residual that is more easily mixed with topsoil components on a large scale than was previously known.
In accordance with the present invention, a new and improved method for reusing water treatment residuals, particularly alum residuals, is provided which overcomes the problems associated with disposal of such water treatment residuals while at the same time producing a blended topsoil with improved physical characteristics.
More particularly, in accordance with the present invention, a process for conditioning alum-type residual comprises dewatering and at least one of the processes of the group consisting of aging and periodically turning. According to this aspect of the invention, residual may be conditioned by mechanically turning over an alum-type residual periodically and exposing the residual to ambient conditions. Periodic turning is believed to insure even dewatering of the residual while simultaneously allowing for the reaction of hydroxide compounds present in the residual. Likewise, the residual may also be conditioned by aging. In such a case, various environmental conditions are allowed to cause the physical breakdown of the gelatinous residual, again allowing for greater conditioning of the residual, including dewatering and reduction of active hydroxide content. A combination of these processes may also be used. Also, any of these processes may be used in conjunction with mechanical dewatering such as dewatering by using mechanical filter presses.
Also in accordance with the present invention, a process for producing an improved blended topsoil comprises the steps of conditioning alum-type residual, particularly alum-type residual, by dewatering and conditioning by aging or mechanically turning or a combination of such processes, removing the processed alum-type residual from the water treatment facility, and blending the processed alum-type residual with topsoil components to create a blended topsoil product. This method is more amenable to large scale use of alum-type residual than previous methods because the method provides a greater level of conditioning of the residual than previous methods. With greater conditioning comes a greater ease of blending the processed residual with other materials. Therefore, the processed residual of the present invention is more amenable to mixing on a large scale to form a blended topsoil than was previously known. The greater conditioning also provides for a decreased likelihood of nutrient binding in the blended topsoil.
According to one aspect of the invention, a blended topsoil includes a concentration of alum-type residual and natural topsoil.
According to another aspect of the present invention, a process for producing blended topsoil includes dewatering the alum-type residual, at least one of the steps consisting of conditioning by aging and turning of the alum-type residual produced by a drinking water treatment facility, testing the alum-type residual for concentrations of trace elements such as aluminum, copper, lead, zinc, and manganese, testing the alum-type residual for a pH greater than or equal to 6.0, and blending the alum-type residual with at least one natural topsoil component to form a blended topsoil.
According to another aspect of the present invention, a process for utilizing alum-type residuals from a water treatment facility includes the steps of dewatering the alum-type residual, conditioning the alum-type residual by at least one of the methods of the group consisting of aging the alum-type residual and periodically turning the alum-type residual, followed by blending the alum-type residual with at least one natural topsoil component to produce a blended topsoil, and using the blended topsoil as a topsoil.
One advantage of the present invention is that the process enables the reuse or recycling of alum-type residuals produced by water treatment facilities without the detrimental effects caused by the presence of active hydroxide compounds in the residual such as nutrient binding.
Another advantage of the present invention is the ability to use alum-type residuals to create a blended topsoil with enhanced physical properties.
Another advantage of the present invention is the ability to utilize alum-type residuals without negatively impacting the environment.
Yet another advantage of the present invention is the avoidance of disposal of alum-type residual in landfills, thereby decreasing the burden placed on such facilities.
Another advantage of the present invention is that an enhanced blended topsoil may be produced that increases the water holding capacity of coarse grained or highly organic materials, while decreasing the compressive strength of the blended topsoil, thereby allowing for greater root penetration by vegetation through the blended topsoil.
Still other benefits and advantages of the invention will become apparent to those skilled in the art to which it pertains upon a reading and understanding of the following detailed specification.